{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"301ec97abf56ebade7fa32d0d43ff7898546fff06ceb23e9527d9dfb1e0bd10b","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["8c1e6a26aac9116250e0401c5f47b9875b097f25daca6f535042b9a3cca997fc","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"595b432303a5167a7513a153a41d63ad2dff404be290c23b04a75bfd6964357d","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":["ai:gpt-5.5"],"external_id":"cm.one-over-f-noise.flux-noise-spins","kind":"well-posed","literature_status":"partially-resolved","n":"2","parents":[],"plain":"Superconducting loops show slow magnetic-flux fluctuations of nearly the same size whatever the loop size or material. Unpaired electron spins on surfaces are blamed, but what they are and how they produce a 1/f spectrum is not settled.","posed_since":"1987","precise":"Low-frequency flux noise $S_{\\Phi}(1\\,\\mathrm{Hz})^{1/2} \\sim 1-10\\,\\mathrm{micro}-\\Phi_0/\\mathrm{Hz}^{1/2}$ ($\\Phi_0=hc/2e$), weakly dependent on loop area, is attributed to surface spins of density $\\sim 5 \\times 10^{13}\\,\\mathrm{cm}^{-2}$ (Koch, DiVincenzo and Clarke 2007). Identify the spin species (adsorbed $\\mathrm{O_2}$, hydrogen, dangling bonds) and the dynamics producing $1/f$ (spin clusters, spin-glass dynamics, spin diffusion), consistent with the measured temperature dependence and the correlation between flux noise and inductance noise.","problem_ref":"8c1e6a26aac9116250e0401c5f47b9875b097f25daca6f535042b9a3cca997fc","references":"","settled_by":"Surface treatments that remove a candidate species and reduce flux noise by the predicted amount, together with a spin model reproducing spectrum, temperature dependence and cross-correlations.","status_note":"Experiments since 2016 link part of the noise to adsorbed molecular oxygen; the spin dynamics producing 1/f remain disputed.","title":"Microscopic origin of 1/f flux noise in SQUIDs and 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